Michael Risner

Publication Date

8-2005

Advisor(s) - Committee Chair

Joseph Bilotta, Steven Haggbloom, Elizabeth Lemerise

Comments

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Degree Program

Department of Psychology

Degree Type

Master of Arts

Abstract

The zebrafish (Danio rerio) has become an important vertebrate model for investigating visual processing. Psychophysical measure of color vision is a useful method to assess the retinal circuitry involved in visual processing. However, visual processing of the zebrafish has received little psychophysical investigation. Anatomical and electrophysiological data suggest zebrafish meet the criteria for color vision: zebrafish have at least two distinct cone photoreceptor types and the neural circuitry that compares the cone inputs (opponent mechanisms). In fact, electrophysiological measures show that zebrafish possess four distinct cone photoreceptors (ultraviolet-, short-, middle-, and long-wavelength sensitive cone types (UV-, S-, M-, and L-cones, respectively)) and two opponent mechanisms (the middle-wavelength minus short-wavelength mechanism (M – S) and long-wavelength minus middle-wavelength (L – M)). This study obtained behavioral spectral sensitivity functions for adult zebrafish. Individual zebrafish were trained in an appetitive three alternative choice discrimination-learning task to monochromatic lights. Once fish were trained, an adaptive staircase method was implemented to obtain visual sensitivity values for each wavelength of light from 340 to 640 nanometers (nm) in 20 nm steps. The results obtained suggest that zebrafish can be instrumentally conditioned within this appetitive instrumental conditioning paradigm. However, zebrafish do not necessarily transfer to subsequent test stimuli. Also, visual thresholds obtained by the adaptive staircase method are comparable to those obtained by deriving psychometric functions. The behavioral spectral sensitivity functions obtained show contributions from two nonopponent cone mechanisms (UV- and UV + S-cones) and two opponent mechanisms (M – S and L – M), a finding that is qualitatively similar to that obtained from physiological measures of spectral sensitivity. However, the behavioral and physiological spectral sensitivity functions are quantitatively different; the suggestion is that further visual processing takes place beyond the processing of the retinal circuitry and optic tectum (the initial processing center in the lower vertebrate brain), thus suggesting that to obtain an accurate assessment of visual processing within an organism, processing must be assessed at both behavioral and physiological levels. Finally, these results demonstrate that the zebrafish is an excellent model in which to examine these issues.

Disciplines

Psychology | Social and Behavioral Sciences

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